4 Project Objectives Scientific objectives Development and design of Mid Temperature Direct Flow Solar Vacuum Tube (SOLEGLASS) that will: Supply the heat in the temperature range C for power generation Accommodate thermal expansion of the assembly while in service Ensure reliable vacuum retention to ensure efficiency Decrease initial material cost for the solar tube production and reduce tube assembly costs 2 Design have been explored: Taking in account all reasons mentioned in project objectives All Glass Tube will be developed in two variants: SOLEGLASS-L for lower medium temperature range ( C) to be applied with related CPC (Compound Parabolic Concentrator) collector SOLEGLASS-H for higher medium temperature range ( C) to be applied with related CSP (Concentrated Solar Power) collector Current Direct flow CPC Current CSP

7 Optimisation of the glass tube Optimising the number of waves n towards stress reduction. Kept constant d = 15mm, b = 5mm, t = 4mm The longitudinal stress tends to decrease exponentially to reach a constant value. In the final design n was chosen to be 4 due the limitation of the mould dimensions

8 Coating technology The efficiency of the heat transfer is also improved using an absorber coating on the inner tube 2 routes were explored for the absorber coating: Air-Sprayed (Solekote ) 92% of absorbance Plasma coated (PVD process) 98% absorbance Plasma coated tube

9 Vacuumation and gettering Gettering: The tubes must be evacuated to minimise heat losses. A getter is used to keep a nearly constant vacuum level. Vacuumation: The tube is evacuated using a pump and the glass tube is melted to produce a seal.

10 CPC Collector

11 Design of the collector Support system design. CPC reflector design Study the effect of the tube geometry (tube and bellow) on the absorbed irradiance. Stepped mirror configuration to accommodate the bellow. Two parabolic mirror geometries

12 Design of the reflectors Bellow peak Inner tube The working fluid is circulating in the inner tube. The heat exchange is maximised where the radiation intensity is highest. In this case the design is not optimised

13 Optimisation of the mirror shape Optimised shape found in the literature (Joshep J. O Gallagher et. al) Extended cusp V groove Which is the most suitable?

14 Energy gained on the absorber at 1000W/m 2 according to various incident angle V_groove Extended_cusp Configuration Irradiance on the absorber over a day (KW h/m 2 ) 500 W/m Extended cusp V-groove Incident angle

15 Final assembly of the reflector No applicable V-groove for r outer 2r inner V groove for the tube and Extended cusp for the bellow ends

16 CPC assembly Support system design. Components for 10-tubes collector How to connect the tubes together? Piping elbows

17 The Houskeeper seal is a standard method to create a chemical bond between glass and metal. Glass-to-metal seal A oxide layer is created on the metal and the glass subsequently melted on this oxide layer to achieve a joint. Skilled operator required Joint durability may be an issue Not suitable for CPC design Mechanical attachment of the parts was preferred.

20 Temperature ( C) Thermal profile 200 Tmax:200 C Left end metal Left inner glass pipe Right end metal Right inner glass pipe Outter glass pipe Bottom lid Tray Time (min) The inflexion point on the curves is due to the use of fans No appearance of crack, failures, or leaks in the assembly or joint

22 Mechanical testing of glass bellows (a) Failure in compression -1.91kN / -0.54mm (b) Failure in tension 4kN / 1.38mm The mechanical properties are within the required range to cope with the anticipated deformation while in service

23 Leak tightness The joints in the assembly were leak tested in an air furnace. The vacuum was drawn in the assembly. The joints were tested with He Air furnace 200 C Stainless cap Glass tube Stainless tube Leak tester Temperature at the joint Leak rate (mbar.l/s) Pressure (bar) 22 C Oil Leak tight when leak rate below mbar.l/s 200 C Leak tight!

26 Structural simulation Collector tilted by 0 C Stress profile due to the inertia of the weight Max: 24.7MPa Collector tilted by 70 (position with the maximal windage) Stress profile due to the inertia of the weight in addition to wind loads (600Pa ~ 112km/h) Max 125.1MPa Below the Yield strength of the reflector and steel ( MPa)

27 Progress The project ends on 31 st August 2014 The consortium is taking the following actions to complete the project: Manufacture of two full-scale 7-tube CPCs to be tested in Croatia and Macedonia Manufacture of a full-scale CSP to be tested in Croatia Acquisition of thermodynamic data Demonstration by the end of the project

28 Project output on completion Technology to convert solar radiation into heat/power Ready for small and industrial scale heating Manufacturing methodology Field trials Videos Final reports and PUDF Exploitation plan and full cost model

29 Acknowledgments The research leading to these results has received funding from the European Union Seventh Framework Programme [FP7/ ] under grant agreement no Copyright Soleglass All Rights Reserved.